Process for the adjustment of the distance between the electrodes of operating electrolysis cells



Nov. 25. 1969 J. M. czuamzm 3,480,528

1 PROCESS FOR THE ADJUSTMENT OF THE DISTANCE BETWEEN THE ELECTRODES 0F OPERATING ELECTROLYSTS CELLS Filed Sept. 1. 1965 1115mm .THICKNEZSS..*J

INVENTOR.

JEAN MAX CLEM ENT FRANCIS M. CRAWFORD ATTORNEY United States Patent Int. Cl. B01k 3 /00; C2211 N04 US. Cl.- 204-99 7 Claims ABSTRACT OF THE DISCLOSURE Method of accurately setting a desired gap between the anodes and mercury cathode of an electrolytic cell by immersing each anode in the mercury cathode, thereby short circuiting it during operation of the cell and sensing the electrolytic current or potential upon withdrawal of the individual anodes and determining cessation of the established short circuit, said cessation of short circuit corresponding to a point at which each anode is again efiective as an active electrode. This is a reference point to be used for spacing the individual anodes a vertical distance from the cathode representative of the optimum gap corresponding to the optimum yield of the cell.

The present invention relates to an improved method for adjusting the distance between the electrodes of operating mercury cells.

It is well known that when conducting electrolyses using mobile mercury cathodes the graphite anodes are eroded with the result that the increase of the distance bet-ween the electrodes causes a decrease in the energy yield of the cell. For this reason it is desirable to adjust periodically the distance between the anodes and the mobile mercury cathode.

In Belgian Patent No. 554,895 the applicant proposed to adjust, while in operation, the distance between the electrodes by taking successively the graphite anodes by their supporting rods and current inlet and moving them toward the mercury cathode until a sharp variation of the current intensity takes place, and particularly when the anode and the cathode are short-circuited, and then moving them apart until the optimum yield of the electrolysis cell is again obtained.

According to this process there is established a geo-' metric point of reference, i.e., the point at which the short-circuit takes place, departing from which the adjustment is effected. Because of the fact that the anode is under electrolysis voltage it is surrounded by a blanket of chlorine gas since the electrolysis continues and the shortcircuit can only be produced when this blanket of chlorine disappears. The depth of the immersion of the anodes in the mercury depends upon the density of the current as well as the shape and also the degree of erosion of the graphite anode. It is in order to avoid this difficulty that the applicant proposed, in Belgian Patent No. 642,974, a process for adjusting the electrodes in which the reference position point for the adjustment is always the same irrespective of the charge of the cell and the degree of erosion of the graphite anode. According to this process, the copper divider connecting the bottom of the precding cell to the series of anodes to be adjusted is opened, so that the latter then being no longer under electrolysis voltage, there can then be inserted between the anode to be adjusted and the mercury cathode any known means suitable for measuring a current and/or a voltage. The anode is taken by its supporting rod and inlet and moved toward the mercury cathode until a sharp 3,480,528 Patented Nov. 25, 1969 drop of voltage occurs, which takes place when the lower part of the anode comes in contact with the surface of the mercury and the anode is then raised a distance corresponding essentially to the optimum yield of the cell.

This latter process accordingly permits attaining a high degree of precision of adjustment. Nevertheless, on account of the necessity for disconnecting the anode, it requires the use of additional labor and the inlet current contacts are subject to additional wear and tear, thus causing an increase in the cost of maintenance. Furthermore, on account of the necessity for disconnecting the rows of anodes, the chlorine arbsorbed upon the disconnected anodes can eventually be desorbed during adjustment of the first anodes, which can cause certain difficulties at the time of their adjustment, a difiiculty which can be overcome by resetting the row of anodes at electrolysis voltage before the adjustment of each of the anodes of the row individually; however, the difficulties referred to above are increased.

The process of the present invention combines the advantages of these two previous processes, i.e., the precision and economy of labor and maintenance, while avoiding their inconveniences.

The new process for the adjustment of the distance between the electrodes in operating mercury cells consists in interposing between the anode to be adjusted and the mobile cathode any knownmeans suitable for measuring a current and/or a voltage, taking the anode under voltage by its supporting rod and current inlet and moving it toward the mobile cathode in order to bring it into contact with this latter at the point when the actual shortcircuit takes place, and removing it to a position corresponding substantially to the optimum yield of the cell. The process is characterized by determining the point when, during its removal, the anode leaving the surface of the mercury, functions again as an. active electrode, this point in fixing in a precise manner the reference point from which the adjustment is eflected.

A preferred variation of the process comprises immersing the anode in the mercury cathode to the point where it comes in contact with the metal bottom, which produces an advantageous cleaning of the bottom and of the cathode.

From the point at which the anode again becomes active its movement is continued until the distance between the electrodes is adjusted to the desired value. By operating in this manner, the adjustment is rendered completely independent of the cell charge; moreover, by operating in this manner there is eliminated the inaccuracies of adjustment due to the mechanical play which any device will show when used for this type of operation.

The determination of the point at which the anode leaves the surface of the mercury (amalgam), i.e., the determination of the reference plane formed by the free surface of the cathodic mercury, is efiected by measuring the abrupt change of the voltage which is inevitably produced when the anode which is no longer in shortcircuit with the cathode, functions again as an active electrode. Any apparatus suitable for this measurement can be used, but it is preferred to use for this purpose a device made of a capacitor (e.g. having a capacity of 40 microfarads) connected in series with a measuring device such as a microammeter, or a galvanometric relay. The use of the latter is particularly advantageous, because in this manner the adjustment operation can be made automatic, the impulses necessary for the systems operation assuring the movement of the anode after the sharp variation of voltage has occurred; furthermore, in this manner errors due to the reading of the apparatus are reduced and thus the transmission of the signals now requires less time. Finally, the apparatus consisting of a capacitora detecting apparatushas the advantage of being sensitive only to changes between the anode and the cathode, regardless of the absolute value of this voltage. It is thus possible to operate without the necessity of making adjustments for different conditions under which the electrolysis may operate.

The invention can be further illustrated by reference to the attached drawing in which FIGURE 2 shows the essential lay-out of the detector apparatus in which MC represents a conventional mercury cell in which Hg represents the mercury cathode, G the movable anode, C a capacitor and R a galvanometric relay. The anode is raised and lowered by a motor not shown. FIGURE 1 illustrates the conditions of operation.

When the detector system is put into operation the capacitor C and the galvanometric relay R automatically start the motor which lowers the movable anode G. When the latter is lowered into contact with the mercury cathode, the capacitor C is partially discharged and, after an adjustable delay the galvanometric relay automatically raises the anode. During the lowering of the anode, the electrical contact with the cathode is established at a point A (FIGURE 1), which does not coincide with the level of the mercury. The point A cannot advantageously be chosen as the point of reference for regulation of the distance of the electrodes when the cell is under voltage, since it depends on numerous factors and, especially on the presence of chlorine gas beneath the anodic surface, the current density, and the effective shape of the anode.

At the time the anode is raised, the point B where the latter is repolarized so that it can again become an active electrode, coincides very closely with the level of the mercury film, which has a thickness of 3 mm. in the example shown (FIG. 1). At the exact moment when the anode leaves the mercury film (reference point B, FIG. 1), the capacitor C (FIG. 2) and the galvanometric relay R put into operation a limitation of the anoderaising movement (time delay of the motor operation or mechanical system with s travel-limiting switch) which brings said anode to the predetermined optimum distance, indicated in the chosen example by d (d representing the original distance of the anode from the cathode).

What is claimed is:

1. A method for decomposing a substance decomposable by an electric current in an electrolytic cell having a liquid cathode and a movable anode which comprises, providing a substance decomposable by electric current in an electrolytic cell, disposing said substance in an electrolytic cell having in operation a liquid cathode and a movable anode in spaced relationship, applying a voltage to said cathode and said anode to develop an electrolytic current flow through said substance, at least periodically adjusting the distance between said anode and liquid cathode without interruption of electrolysis in said electrolytic cell by advancing said anode through said substance being decomposed electrolytically and in a direction to approach the cathode until the electrolytic current of said cell undergoes a rapid increase disproportionate to the speed of said advancing and corresponding to an immersion of said anode in said cathode and an indication of a complete short circuit between said anode and said cathode, during said advancing detecting said rapid increase of said electrolytic current, and then displacing said anode in an opposite direction until the electrolytic current of said cell undergoes an abrupt change corresponding to cessation of said short circuit and a withdrawal of said anode from said cathode, and corresponding to a point at which said anode is effective again as an active electrode, during said displacing of said anode in an opposite direction detecting when said abrupt change takes place and displacing said anode in said opposite direction from the point at which said abrupt change is detected to a vertical distance spaced from said mercury cathode substantially corresponding to the optimum yield of said cell.

2. A method for operating an electrolytic cell for electrolysis of an aqueous solution decomposable into a gas and other components by an electric current and having an-electrically conductive liquid cathode and a movable anode spaceable relative to the cathode and movable toward and away from said cathode which com prises, advancing during operation of the cell said anode through said aqueous solution and said gas in a direction to approach the cathode until the electrolytic current undergoes a rapid increase corresponding to an immersion of said anode in said cathode and an indication of a complete short circuit between said anode and said cathode, during said advancing of said anode detecting said rapid .increase of said electrolytic current and then displacing said anode in an opposite direction until the electrolytic current of said cell undergoes an abrupt change corresponding to cessation of said short circuit and a withdrawal of said anode from said cathode, and corresponding to a point at which said anode is elfective again as an active electrode during said displacing of said anode in .1811 opposite direction detecting when said abrupt change takes place and displacing said anode in said opposite direction from the point at which said abrupt change is detected to a distance spaced from said mercury cathode substantially corresponding to the optimum yield of said cell.

3. A method for operating an electrolytic cell according to claim 2, in which said anode reaches and touches the bottom of said cell before being displaced in said opposite direction.

4. A method for regulating during operation the distance between a graphite anode and a mercury cathode in an electrolytic cell for electrolysis of aqueous solutions which comprises, advancing during operation of the cell said anode in a direction to approach the mercury cathode until the electrolytic current undergoes a rapid increase indicative of an immersion of said anode in said cathode and thus indicative of a complete short circuit between said anode and said cathode, during said advancing of said anode detecting said rapid increase of said electrolytic current and then displacing said anode in an opposite direction until the electrolytic current of said cell undergoes an abrupt change corresponding to a point at which said anode is effective again or an :active electrode and withdrawal of said anode from said cathode and cessation of said short circuit, during said displacing of said anode in an opposite direction detecting when said abrupt change takes place and displacing said anode in said opposite direction from the point at which said abrupt change is detected to a distance above said mercury cathode substantially corresponding to the optimum yield of the cell.

5. A method for regulating during operation the distance between a plurality of graphite anodes and a mercury cathode in an electrolytic cell for the electrolysis of aqueous solutions, which comprises consecutively advancing said anodes individually in a direction toward said mercury cathode until a portion of the individual anode makes contact with said mercury cathode and is immersed therein and the electrolytic current undergoes a rapid increase indicative of an immersion of said anode in said cathode and thus indicative of a complete short circuit between said anode and said cathode, during said advancing of the anodes sensing the electrolytic current of said cell, and then retracting the individual anodes in the opposite direction away from said mercury cathode until the electrolytic current of said cell undergoes an abrupt change corresponding to withdrawal of said anode from said cathode and a cessation of said short circuit, and corresponding to a point at which said anode is effective again as an active electrode, during retracting the anodes in an opposite direction detecting when said abrupt change takes place, and retracting the individual anodes in said opposite direction from the point at which said abrupt change is detected to a distance above said mercury cathode substantially corresponding to the optimum yield of the cell.

6. A method for operating an electrolytic cell for electrolysis of an aqueous solution decomposable into a gas and other components by an electric current and having an electrically conductive liquid cathode and a movable anode spaceable relative to the cathode and movable toward and away from said cathode which comprises, advancing during operation of the cell said anode through said aqueous solution and said gas in a direction to approach the cathode until a complete short circuit occurs between said anode and said cathode, during said advancing of said anode detecting said short circuit by detecting when said anode ceases to function as an effective anode in eifecting said electrolysis and then displacing said anode in an opposite direction until cessation of said short circuit, during said displacing of said anode in an opposite direction detecting when said anode functions as an eflective anode in efiecting said electrolysis thereby to detect withdrawal of said anode from said cathode and cessation of said short circuit, and displacing said anode in said opposite direction from the point at which said cessation of said short circuit is detected to a distance spaced from said mercury cathode substantially corresponding to the optimum yield of said cell.

7. A method for operating an electrolytic cell for electrolysis according to claim 6, in which said anode is advanced toward said cathode until it touches the bottom of said cell.

References Cited UNITED STATES PATENTS JOHN H. MACK, Primary Examiner D. R. VALENTINE, Assistant Examiner US. Cl. X.R. 204-219, 225, 250 

